1. Field of the Invention
The present invention relates to warm white LED technology and more particularly, to an InGaN substrate-based warm white LED comprising a great number of nanograde lutetium-based phosphor.
2. Description of the Related Art
US engineers H. Yooder and M. Kettle firstly introduced a synthetic crystalline material of the garnet group containing Y3Al5O12, and gave the material the name of Yttrium aluminum garnet (YAG).
Yooder teaches the structural space composition of the synthetic crystalline material to be a J103d synthetic garnet of which the lattice parameter a=12.01±0.2 Å is greater than natural garnet a≈11.86 Å. Large size Y+3 and Mn+3 were used together in the material. This material has the chemical formula A3B2(BO4)3, in which A type ions (rare earth elements, such as calcium, iron, etc.) have a dodecahedral coordination with the coordination number Ku=8; B type ions (silicon and partial aluminum) have the coordination number Ku=4; a part of Al+3 ions have an octahedral structure with coordination number Ku=6.
Ever since a long time ago, people's attention is focused on the beautiful ruby. Yooder opened the door of synthesis and created a new technology of industrial crystallization. This technological concept was developed in 20th Century and joined with laser technology for application.
U.S. Pat. No. 3,882,215 and CA900620A disclosed phosphor-contained light emitting diodes based on GaP—GaAs to radiate in the infrared spectrum, enabling the invisible infrared radiation to be converted into visible red light, green light or blue light by means of an Anti-Stokes phosphor.
In 1994, Japanese physicist S. Nakamura introduced the use of a Stokes phosphor in GaN semiconductor architecture (see S. Nakamura Blue laser Sringer-Verlar Berlin 1997) to enhance the performance. Shortly thereafter, in 1995, a Nichia's physicist introduced a white light LED using a wideband phosphor Y3Al5O12:Ce (see U.S. Pat. No. 3,564,322, GB 1174518, DE1764218 and Be714420) and a light-emitting diode synthetic structure (U.S. Pat. No. 3,564,322, GB 1174518, DE1764218 and Be714420). The concept is based on the theory of color developed by Isaac Newton (1642˜1727) to create white radiation by means of combining two complementary colors. In the well-known patent N5988925, there are many drawbacks as follows: 1. The luminous efficacy of the light-emitting diode is low, or about 10˜12 lumen/watt when the color temperature is over 5000K; 2. InGaN light-emitting diode's blue radiation produce adverse effects to vision; and 3. It is difficult to duplicate warm white light by using a solid (Y,Gd,Ce)3Al5O12 substrate-based single-component material.
Due to lack in single-component garnet structure-based light-emitting material, development of warm white light-emitting diode is limited. Using a single-component (Gd,Ce)3Al5O12 to construct a similar light-emitting diode has not yet been confirmed. Further, series of researches with the use of single-component phosphor Gd3Al5O12 were denied by Aedred F. A (Aedred F. A Trans Brit Ceram Soc. 1959. vol 58N4p 199-210).
Using Y3Al5O12:Ce and CaAlSiN3:Eu two-component phosphor to make a warm red light-emitting diode has been disclosed (US2008283801A, Nov. 20, 2008 and Soshchin N's CN 2008 1016492, Nov. 5, 2008). In these disclosures, many garnet structures are introduced for obtaining warm white light. Along these disclosures, CN 20081016492 is likely to be deemed relevant to the field of the invention.